Geez, it's funny how things get simplified, turned around, and misconstrued after in such a short time.
For the record, my position, based mainly on my instructor's comments as well as my own experience is that one can reach a BASIC LEVEL OF PRFICIENCY in about a year of practice. My instructor was able to not only defend himself, but do so in such a way that the other guy was unhurt after about that much time studying.
Now, your milage may vary. I personally feel pretty comfortable with my basic body movements and my ability to get out of the way of an attack. These things are bourne out in practice in the dojo. I'm not sure I could pull off a technique outside the dojo, and frankly don't worry about it too much. I don't think I'm at the level of proficiency that my instructor had after the same amount of study, though.
I said nothing about becoming a shodan, nor did I equate being able to defend oneself successfully with being a shodan as Cas seems to be doing. I also realize that different dojos are different. I come from a small dojo where we have a lot of one-on-one attention with the sensei. That may give us the ability to do some things that might be difficult for lower ranks in larger classes.
All I know is that we focus on principles as nage, and presenting strong, committed attacks as uke. I also know that being basically proficient in an art is not the same as having mastered it. I know I have many many many years ahead of me as an aikidoka -- and that's a comforting thought.